DNA binding proteins play an important role in processes such as replication and repair of DNA, as well as transcription activation and termination. Many transcription factors bind to a specific DNA site (or sites) and as a result of this specific binding the factors regulate important metabolic functions such as cell growth development and differentiation. There is great interest in understanding the function of those regulatory proteins, especially when the role of the transcription factors is linked to oncogenesis. The PU.1 transcription factor is a member of the ets gene family and is identical to the spi.1 oncogene. The PU.I gene, as well as other members of the ets family have been implicated in oncogenic processes such as the development of erythroid leukemia. Recent studies suggest that ets proteins contribute to tumorigenesis in breast cancers. The ets proteins share a conserved region of approximately 85 amino acids (the ETS domain) that serves as a DNA binding domain and recognizes a purine-rich sequence-with the core sequence: 5-GGAA/T-3. The sequence of the ETS domain represents a new, yet uncharacterized DNA-binding motif, with no homology to other DNA- binding structures. The goals of this project are to use a combination of molecular biology, nuclear magnetic resonance (NMR) and x-ray crystallography to examine sites in the PU.I protein that mediate specific DNA recognition. Atomic models will be used to understand the molecular basis for the function of ets-related transcription factors and to evaluate the role of these regulatory elements in the development of leukemia, breast cancer, and other cancers.